Re: [dpdk-dev] [PATCH 3/4] eal/arm: Enable lpm/table/pipeline libs

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

On Thu, Dec 03, 2015 at 11:02:07AM +0000, Ananyev, Konstantin wrote:

Hi Konstantin,

> Hi Jerin,
>
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jerin Jacob
> > Sent: Thursday, December 03, 2015 9:34 AM
> > To: Thomas Monjalon
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH 3/4] eal/arm: Enable lpm/table/pipeline libs
> >
> > On Wed, Dec 02, 2015 at 05:57:10PM +0100, Thomas Monjalon wrote:
> > > 2015-12-02 22:23, Jerin Jacob:
> > > > On Wed, Dec 02, 2015 at 05:40:13PM +0100, Thomas Monjalon wrote:
> > > > > 2015-12-02 20:04, Jerin Jacob:
> > > > > > On Wed, Dec 02, 2015 at 09:13:51PM +0800, Jianbo Liu wrote:
> > > > > > > On 2 December 2015 at 18:39, Jerin Jacob <jerin.jacob@caviumnetworks.com> wrote:
> > > > > > > > AND they include "rte_lpm.h"(it internally includes rte_vect.h)
> > > > > > > > that lead to multiple definition and its not good.
> > > > > > > >
> > > > > > > But you will have similar issue since "typedef int32x4_t __m128i"
> > > > > > > appears in both your patch and this header file.
> > > > > >
> > > > > > I just tested it, it won't break, back to back "typedef int32x4_t __m128i"
> > > > > > is fine(unlike inline function).
> > > > > >
> > > > > > my intention to keep __m128i "as is"  because changing the __m128i to rte_???
> > > > > > something would break the ABI.
> > > > >
> > > > > Isn't it already broken in 2.2?
> > > >
> > > > Does it mean, You would like to have rte_128i(or similar) kind of
> > > > abstraction to represent 128bit SIMD variable in DPDK?
> > >
> > > If you are convinced that it is the best way to write a generic code, yes.
> >
> > I grep-ed through DPDK API list to see the dependency with SIMD in API
> > definition.I see only rte_lpm_lookupx4 API has SIMD dependency in API
> > definition.
> >
> > I believe that's the root cause of the problem. IMO, The
> > better way to fix this would be to remove __m128i from API and have more
> > general representation to remove the architecture dependency from API
> >
> > something like this,
> >
> > rte_lpm_lookupx4(const struct rte_lpm *lpm, uint32_t *ip, uint16_t
> > hop[4], uint16_t defv)
> >
> > instead of
> >
> > rte_lpm_lookupx4(const struct rte_lpm *lpm, __m128i ip, uint16_t
> > hop[4],  uint16_t defv)
>
> The idea for that function was that rte_lpm_lookupx4() accepts 4 IPv4 addresses that are:
> 1. already in 128bit register
> 2. 'prepared' - byte swap is already done for them if needed.
>
> About ways to fix  __m128i dependency: as I can see x86 and arm DPDK code
> already has xmm_t typedef:
>
> $ find lib -type f | xargs grep xmm_t | grep typedef
> lib/librte_eal/common/include/arch/x86/rte_vect.h:typedef __m128i xmm_t;
> lib/librte_eal/common/include/arch/arm/rte_vect.h:typedef int32x4_t xmm_t;
>
> Why not to  change rte_lpm_lookupx4() to accept xmm_t as input parameter.
> As I understand it would solve the problem, and wouldn't introduce any API/ABI breakage, right?

Yes, If we have API/ABI breakage concerns.

IMO, Now this would call for some kind of rte_vect_* abstraction load,
store, set kind of SIMD operation on xmm_t in common test code to
aviod #ifdef's in app/test/test_lpm.c

I guess we may not need those abstractions in
lib/librte_eal/common/include/arch/ directory.
keeping in app/test/xmmt_ops.h should be enough, right?


>
> Konstantin
>
> >
> > Now I am not sure why this API was created like this, from l3fwd.c
> > example, it looks to accommodate the IPV4 byte swap[1]. If it's true,
> > maybe we can have eal byte swap abstraction for optimized byte swap on
> > memory for 4 IP address in one shot
> >
> > or
> >
> > Have rte_lpm_lookupx4 take an argument for byte swap or not ?
> >
> > or
> >
> > something similar?
> >
> > Thoughts ?
> >
> > [1]
> > const  __m128i bswap_mask = _mm_set_epi8(12, 13, 14, 15, 8, 9, 10, 11,
> >                                                 4, 5, 6, 7, 0, 1, 2, 3);
> > /* Byte swap 4 IPV4 addresses. */
> > dip = _mm_shuffle_epi8(dip, bswap_mask);
> >
> > Jerin
> >
> > > I think the most important question is to know what is the best solution
> > > for performance and maintainability. The API/ABI questions will be considered
> > > after.
> > >
> > > Thanks for your involvement guys.